The present invention relates to plate pushing devices for wood working equipment, and in particular to a plate pushing device positioned on a horizontally-movable carriage for pushing plate-shaped workpieces off of a lifting platform, into woodworking machines such as plate saws. The present invention also relates in particular to plate pushing devices which include a vertically movable pushing element, that is directed against an edge of one or more workpiece plates and which is arranged to move vertically with a support member that rides along the surface of a workpiece plate, during the pushing motion of the pushing element, to maintain the pushing element at least a constant predetermined distance above the uppermost remaining workpiece plate on the lifting platform, to preclude injury to the upper surface of the uppermost remaining workpiece plate.
An example of a prior art plate pushing device may be seen in U.S. Pat. No. 4,726,724 to Jenkner, issued Feb. 23, 1988 claiming priority of German Patent Application No. DE35 15 729. In these references, a plate pushing device is disclosed in which a pushing element (feed member) is movably supported on a vertical guide which is carried on a horizontally movable carriage. The pushing element (feed member) is selectively fixable along the vertical guide by clamping means. A support member is also arranged within the carriage for movement along a vertical guide. Clamping means are provided to enable selective fixing of the support member at any position along its vertical guide, as well. Accordingly, the support member is operably coupled to the pushing element by such clamping means so that the support member and pushing element so as to move in tandem along the vertical direction.
Attached to the forward end of the support member is a roller that is in contact with the upper surface of the uppermost workpiece plate resting on the lifting platform. The support member also carries a vertically arranged bar shaped information member, which cooperates with a stationary scanning device, to produce an indication of the vertical movement of the pushing device, resulting from the lifting movement of the lifting platform. The indication of the elevation of the lifting device is converted into a signal which is fed into the control for the lifting device for the lifting platform, so that, when the lifting platform has been raised to a height corresponding to the desired number of workpiece plates to be pushed off of the lifting platform, the signal causes the lifting device to stop its lifting movement.
During the lifting movement of the lifting device, the support arm of the prior art plate pushing device is uncoupled from the pushing element, so that the pushing element does not move vertically. After the lifting movement of the lifting device is completed, the support member and the pushing element are again coupled, so that during the subsequent pushing movement of the pushing element, the support member continues to ride atop the uppermost plate of the plate or plates being pushed and maintains the pushing element a substantially uniform distance above the upper surface of the upper workpiece on the stack of remaining workpiece plates. As the workpiece plates being pushed pass over the remaining plates, irregularities in the surface of the uppermost remaining plate will be transmitted through the stack being pushed and cause the support member to move up or down, causing the pushing element to move up or down and remain a predetermined distance above the upper surface of the uppermost remaining plate.
However, such prior art plate pushing devices require at least two clamping means which themselves require the presence of external power supplies and external or automatic control devices for their operation. Such additional devices add to the cost, size, and complexity of the plate pushing device. An additional potential limitation of such prior art plate pushing devices is that they rely upon transmission of the irregularities through the stack of plates being pushed, to the support member, for detection of the irregularities and maintenance of the pushing member the necessary distance above the surface of the uppermost remaining plate to avoid damage to the uppermost remaining plate.
It is, accordingly, an object of the invention to provide a plate pushing device, carried by a horizontally movable carriage, which is equipped with a support member arranged to prevent injury to workpiece plates by the pushing element of the plate pushing device during the pushing movement of the pushing element.
It is an additional object of the invention to provide such a plate pushing device which requires a minimum number of external controls or power supplies, so as to reduce the cost, size, and complexity of the plate pushing device.
Another object of the invention is to provide such a plate pushing device which detects the presence of irregularities in the surface of the uppermost remaining plate directly, to more accurately and consistently maintain the pushing element above the just-described upper surface and preclude damage thereto by the pushing element.
These and other objects of the invention will become apparent in light of the present specification, drawings and claims.